1. Field of the Invention
The present invention relates to a method of processing composite wastes including combustibles and incombustibles such as the bodies of waste cars.
2. Description of Related Art
The recycling of waste articles to effectively utilize limited natural resources has been receiving much attention lately. In some countries, shredder dust, Freon and air bags from waste cars, for example, are designated as recyclables. Of these three articles, shredder dust poses the most formidable obstacle in the recycling of waste cars. Therefore, shredder dust is collected generally by the car manufacturers. Shredder dust is a collection of small pieces of waste materials formed by shredding the body of a car together with the seats and various ornamental materials inside the car. Car manufacturers may commission appropriate contractors to perform final disposal of the shredder dust. As means of disposal, various facilities are planned, such as dry distillation furnaces, carbonization furnaces, incinerators, melting furnaces, blast furnaces, electric furnaces and final disposal dump.
Conventionally, waste cars are processed according to the method shown in FIG. 1. First, the engine, battery, tires, fuel tank, suspension are dismantled from the waste car, leaving the body and mostly ornamental materials inside the car (step S1). The remaining materials, i.e., the body and ornamental materials, are shredded (step S2). The shredded materials are separated into two groups. One is pieces of metals such as iron and aluminum. The other is shredder dust including mainly pieces of combustibles such as plastics and cloth (step S3).
However, a small amount of metal pieces (metal scraps) cannot be separated successfully from the combustibles. That is, a small amount of metal pieces remains in the shredder dust. Then, the combustibles are carbonized by subjecting the shredder dust to dry distillation (step S4).
Conventionally, before performing the dry distillation process, the shredded materials are separated into metal scraps and shredder dust. While efforts to increase the thoroughness of this separation will increase the amount of metal scraps to be collected, it will lead to increased costs for separation. Since the combustible and the incombustibles are connected to each other by cohesive materials, these materials remain connected even after they are shredded into small pieces. So it is difficult to separate them thoroughly by using a magnetic pulling force or the difference in their specific gravities and results in increased costs. Further, heat loss is large, because the shredder dust includes a lot of water. Therefore, much time has been required to distill the shredder dust and expenses are high because a drying device is needed to dry shredder dust having so much water.